The widespread adoption of optical storage products such as the "Compact Disc" (CD) has made it desirable to manufacture these products by processes which have the potential to greatly increase throughput and decrease cost. Optical storage products made by such a process could greatly increase the dissemination of information while reducing the need for paper production with its negative environmental impact and improving the accessibility and archivability of the information.
Continuous processes most notably roll to roll are known to be more effective in making large volumes of products at low cost. The well known "floppy" magnetic disks are one good example of this. In fact rolls of the disk material structures are commonly sold as product in the "floppy industry." However optical disks and other elements are almost exclusively made by discrete batch injection molding based processes. As a consequence of this history several attempts have been made to manufacture optical media in continuous processes. The article "Continuous manufacturing of thin cover sheet optical media" by Slafer et. al. (including the present inventor) in the Proceedings of the SPIE (Vol. 1663 pg. 324) describes one approach. U.S. Pat. No. 4,831,244 ('244) discloses optical card structures with disk patterns made using the approach of this publication. The book, "Optical Recording--a Technical Overview, by Alan B. Marchant, published by Addison-Wesley Publishing Co. 1990 presents a good view of prior art techniques, especially the section on Mastering, page 327. The article in the Proceedings of the SPIE and the book are both hereby incorporated by reference herein as if laid out in full text. In the SPIE article a continuous roll embossing process is used to create optical features on the surface of a substrate which is then coated with appropriate absorptive, active, reflective and or refractive layers to produce functional optical media or elements. Land in U.S. Pat. No. 4,366,235 ('235) describes the general outline of the process of embossing a roll of substrate with appropriate optical features using an embossing drum and fluid. These process steps are characterized as "known in the art". A similar approach is described by Beaujean in U.S. Pat. No. 4,543,225 (225). Another similar approach by Foster U.S. Pat. No. 4,836,874 ('874) uses roll embossing with a fluid that has a dye included for improving the feature forming by absorbing laser light. All of these approaches are characterized by one or more of the following elements: lamination of a thin web to a cover sheet, embossing by a fluid, manufacture of a special embossing drum, and separate processing steps.
The past attempts to manufacture optical media and components in a continuous process have shared the characteristic that they have not been truly continuous but rather have been segmented and in many cases multiple substrate processes. In the case of the above cited U.S. Pat. Nos. '244, '225, and '874, two substrate webs are used and a chemical fluid based embossing process is employed. This requires that the vacuum coating of recording and or reflective layers be done in a separate segmented step.
Another problem associated with a chemical embossing process is the drum used to effect the embossing. If the drum does not have a seamless surface, fluids can accumulate in and flow out of the seams onto the substrate thus destroying the fine structure tolerance features which are necessary for optical grade devices and media. Seamless drums are difficult to fabricate, time consuming, and consequently expensive especially in wide web systems. One would like to use discrete embossing tools individually mounted on a drum as they are easy to manufacture using existing optical mastering and electroforming technology, they allow mounting across web as a means to work with wide webs, and as is disclosed later they can be compensated for distortions resulting from wrapping them on a drums' surface. Also discrete embossing tools can be easily changed for short run, quick turn around situations. An additional problem with earlier processes is the need for an high cleanliness environment laminating step in order to provide a low defect bond line between the thin web which is vacuum coated and the thick web optical cover sheet that provides isolation from surface defects and makes the structure sufficiently rigid and flat.
In an attempt to avoid the consequences of the earlier fluid based embossing U.S. Pat. Nos. 5,423,671, 5,368,789, 5,281,371, 5147,592, and 5,075,060 combine embossing into the process of extruding or molding of a thick substrate. Unfortunately this approach has similar problems to the earlier efforts when it comes to the need for a seamless embossing tool, as now the tool is part of the extrusion process. To achieve proper gauge thickness and tolerance along with avoiding "flashing" into the seams of a drum with discrete tools mounted on its surface is very difficult. As the gauge thickness appropriate to higher numerical aperture optics systems decreases, these problems will magnify. This will compromise the speed of the extrusion process, the bulk material birefringence, and its cost. Most important this approach makes it very difficult to integrate the embossing step into a single continuous vacuum machine as extrusion is combined with embossing. A consequence of this unintegrated process architecture is that the most critical surface in the structure the embossing is vulnerable to damage via handling before the vacuum coatings and protective layers can be added to complete the manufactured structure.
Generally speaking it is essential to avoid the use of fluids or liquids in embossing and to separate the extrusion of the substrate from the embossing step. This eliminates as much as possible the potential for outgassing and other vacuum compromising effects and allows extrusions to be made off line at maximal widths and web speeds. Also it is mandatory that only micron dimensional volumes of material be activated and or enabled to participate in the embossing step thus eliminating the potential for structural compromise like dimensional changes, stress, birefringence, and other distortion producing effects and material movement into interstitial boundaries between discrete embossing tools. These principles are the basis for developing a machine architecture which combines all process steps into one machine, uses a single substrate, and employs individual embossing tools so quick turnaround with high volume is realizable. It is important to emphasize that the novel object of this invention is to create a process architecture compatible with the environment in a vacuum coating chamber not that a vacuum be used to make the embossing. Bussey et. al. in U.S. Pat. No. 3,957,414 disclose the use of a vacuum between a substrate and an embossing "screen", but it is evident that this approach would not work in a vacuum chamber where there would be no gas to apply pressure to the substrate.
Another problem inherent with drum embossing is the distortion due to the curved contour of a drum. While is easy to master rectilinear features directly on a drum tool as would be the case for tape or card stripes, the use of a standard disk mastering recorder is essential to making precision circular tracks as found on disks. This however requires the tools (stampers) to be wrapped around a drum circumference and results in the distortion of the circular track patterns. When a planar tool of finite thickness is wrapped on a drum, patterns on the outside surface are elongated and patterns on the inside are shortened in the circumferential direction. Thus circles become prolate ellipse like patterns on the outside of tools wrapped on a drum. In the case where a substrate is wrapped around the tool and then returned to a flat geometry, the same effect occurs but patterns on the inside are elongated and so the problem is compounded. One solution to this problem is to precompensate for this effect using the mastering machine to record oblate rather than circular track patterns, but this approach has problems and limitations if the substrate is thick (0.1 mm or greater) as will be the case for single substrate disk or card manufacturing processes as contemplated in the preferred continuous single machine.
It is an object of the present invention to provide a method and a single integrated apparatus, which in a single pass continuously embosses and coats a continuous substrate.
It is another object of the present invention to provide a system without using any liquids, or molten/fluid state materials.
It is yet another object of the present invention to provide a conditioning of a substrate immediately prior to embossing, wherein the conditioning prepares the substrate and stamper for impressing the embossing pattern.
Yet another object of the present invention is to provide an embossing process that is compatible with the coating environment, such that the embossing and coating can be accomplished in the same environment.
Another object of the present invention is to provide uninterrupted process starting with a roll of substrate and ending with a roll of finished embossed and coated structures ready for cutting from the web.
Still another object of the present invention is provide a process and apparatus that is compatible with discrete embossing tools as this gives greater flexibility, quicker turnaround with higher volumes and lower cost to the process.
It is still another object of the present invention to provide a single environment wherein the entire embossing and coating is accomplished.
It is still another object of the present invention to compensate for embossing distortion found when embossing using stamper tools with a finite thickness are mounted on drums. A related object is to provide such compensation for distortion effects on a single thick substrate.